A United States appeals court panel in Manhattan yesterday upheld the conviction of a bookmaker who was sentenced to 21 months in prison as part of what the authorities called the first federal prosecution of Internet sports gambling.

The case involved a lucrative Internet sports betting business run by the man, Jay Cohen, from the island of Antigua, in the Caribbean. By November 1998, the venture, World Sports Exchange, had received 60,000 phone calls from customers in the United States, including more than 6,100 from New York, the panel said in its opinion.

Federal prosecutors in Manhattan had charged that Mr. Cohen's enterprise violated a federal law that banned the use of interstate wires for betting.

According to the opinion, customers opened accounts with the company, wired at least $300 to the accounts, and then used the Internet or telephone to authorize the company to place bets for them.

The company took a 10 percent commission for each bet, the opinion said.

In its opinion, a three-judge panel of the United States Court of Appeals for the Second Circuit rejected Mr. Cohen's contentions that the law was unclear and ambiguous, and that his customers were not actually placing bets over the phone lines in violation of the law.

According to the opinion, Mr. Cohen contended that his customers were only conveying information that enabled his company "itself to place bets entirely from customer accounts located in Antigua."

But the panel, ruling unanimously, said the government had proved at trial last year that World Sports Exchange's customers were placing bets.

Mr. Cohen's lawyer, Mark M. Baker, said his client had modeled his business after New York's Off-Track Betting Corporation.

"He took every step imaginable to determine the legality of his action," Mr. Baker said, "and the court has found that all that is irrelevant."

Mr. Baker said that no decision had been made concerning an appeal for Mr. Cohen, who has been free on bail and now lives in California.

In addition to his sentence, Mr. Cohen was also fined $5,000. Prosecutors had no comment yesterday.

The opinion was written by District Court Judge John F. Keenan, who sat by special designation on the appeals panel. The panel also included Judges Pierre N. Leval and Fred I. Parker.